Pre-ignition in a flame propagation (or “spark-ignition”) engine describes an event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.
Many passenger car manufacturers have observed intermittent pre-ignition in their production turbocharged gasoline engines, particularly at low speeds and medium-to-high loads. At these elevated loads, pre-ignition usually results in severe engine knock that can damage the engine. The cause of the pre-ignition is not fully understood, and may in fact be attributed to multiple phenomena such as hot deposits within the combustion chamber, elevated levels of lubricant vapor entering from the PCV (positive crankcase ventilation) system, oil seepage past the turbocharger compressor seals or oil and/or fuel droplet auto-ignition during the compression stroke.
Pre-ignition can sharply increase combustion chamber temperatures and lead to rough engine operation or loss of performance. Traditional methods of eliminating pre-ignition include, for example, proper spark plug selection, proper fuel/air mixture adjustment, and periodic cleaning of the combustion chambers. Hardware solutions such as cooled exhaust gas recirculation (EGR) are known, but these can be costly to implement and present packaging problems.
Low speed pre-ignition (LSPI) is a type of abnormal combustion affecting engines operating at high brake mean effective pressure (BMEP) and low engine speed (RPM). This includes internal combustion engines using a variety of fuels, including natural gas, gasoline, diesel, biofuels, and the like. Downsized, downspeeded, turbocharged engines are most susceptible to operating under these engine conditions and are thus more susceptible to LSPI. As the automobile industry continues to move towards further downsizing, downspeeding, and increased turbocharging to increase vehicle fuel economy and reduce carbon dioxide emissions, the concern over LSPI continues to grow.
The further development of downspeeded, turbocharged gasoline engines is being impeded by LSPI. A solution to this problem or even a mitigation of its occurrence would remove barriers for original equipment manufacturer (OEM) technology and efficiency improvement. A lubricant formulation solution would enable product differentiation with regard to LSPI.
Although pre-ignition problems can be and are being resolved by optimization of internal engine components and by the use of new component technology such as electronic controls, modification of the lubricating oil compositions used to lubricate such engines is desirable. For example, it would be desirable develop new lubricating oil formulations which are particularly useful in internal combustion engines and, when used in internal combustion engines, will prevent or minimize the pre-ignition problems. It is desired that the lubricating oil composition be useful in lubricating gasoline-fueled, spark-ignited engines.
Despite the advances in lubricant oil formulation technology, there exists a need for an engine oil lubricant that effectively prevents or reduces low speed pre-ignition especially for downsized, downspeeded, turbocharged engines while maintaining or improving cleanliness performance.